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Isometric Force (isometric + force)
Selected AbstractsDiabetes-induced Alterations in Latissimus Dorsi Muscle Properties Impair Effectiveness of Dynamic Cardiomyoplasty in RatsARTIFICIAL ORGANS, Issue 4 2004Kátia De Angelis Abstract:, Short-term diabetes was induced in male Wistar rats with streptozotocin injection. The effects of diabetes on latissimus dorsi (LD) muscle contractile and biochemical properties and acute cardiomyoplasty (CDM) were assessed and compared with data from 16 control rats. Isometric force, contractile properties, and fatigue were measured in electrically stimulated muscles (0.3 ms, 1,256 Hz), and Na+K+ and Ca2+ATPase activities were quantified in muscle membrane preparations. Systolic arterial pressure and aortic blood flow were recorded at rest and during LD muscle stimulation. Compared with control muscle, diabetic muscle showed smaller maximum specific tetanic tension and lower rates of rise and fall in force. Diabetic LD muscle also showed lower muscle enzyme activities. Twitch tension and fatigue did not differ between groups. Smaller increases in aortic flow and systolic pressure after CDM were found in diabetic rats compared to controls. The marked decrease in CDM effectiveness in diabetic rats likely reflected the alterations in muscle properties associated with diabetes. [source] The effect of number of lengthening contractions on rat isometric force production at different frequencies of nerve stimulationACTA PHYSIOLOGICA, Issue 3 2009M. E. T. Willems Abstract Aim:, To test the effect of 3, 10, 60 and 240 lengthening contractions (LC) on maximal isometric force of rat plantar flexor muscles at different stimulation frequencies. Methods:, Using a dynamometer and electrical nerve stimulation, maximally active skeletal muscles were stretched by ankle rotation to produce LC of the plantar flexor muscles in intact female rats. After the lengthening contraction protocols, maximal isometric force was measured at different frequencies of nerve activation to obtain frequency-dependent force deficits (weakness). Results:, The magnitude of the force deficit, measured 1 h after the protocols at 80 Hz, increased as a function of repetition number (three LC, 33.3 ± 1.7%; 10 LC, 37.2 ± 2.3%; 60 LC, 67.6 ± 1.5%; 240 LC, 77.7 ± 1.2%). Force deficits were also measured at each stimulation frequency tested (5:120 Hz). Using a ratio of isometric force at 20:100 Hz stimulation, the relative depression of force at low frequency was determined. The relative depression of isometric force at low frequency was most prominent during the early repetitions. Conclusion:, As low-frequency force depression appears to result primarily from excitation,contraction (E,C) coupling failure, the early LC in a series of repeated contractions probably contribute most to damage of the cellular components involved in E,C coupling. [source] Effects of supra-physiological changes in human ovarian hormone levels on maximum force production of the first dorsal interosseus muscleEXPERIMENTAL PHYSIOLOGY, Issue 2 2005Kirsty Jayne Elliott The purpose of this study was to investigate the effects of supra-physiological changes in ovarian hormone levels on maximum force production in two conditions, one physiological (pregnancy) and one pseudo-physiological (in vitro fertilization (IVF) treatment). Forty IVF patients were tested at four distinct stages of treatment and 35 women were tested during each trimester of pregnancy and following parturition. Maximum voluntary isometric force per unit cross-sectional area of the first dorsal interosseus muscle was measured. Plasma concentrations of total and bioavailable oestradiol and testosterone were measured, in addition to the total concentrations of progesterone and human chorionic gonadotropin. Despite significant changes in the concentrations of total progesterone, 17,-oestradiol, bioavailable oestradiol and testosterone between phases, strength did not change significantly throughout IVF treatment (1.30 ± 0.29, 1.16 ± 0.38, 1.20 ± 0.29 and 1.26 ± 0.34 N mm,2, respectively, in the 4 phases of IVF treatment). Force production was significantly higher during the second trimester of pregnancy than following childbirth (1.33 ± 0.20 N mm,2 at week 12 of pregnancy, 1.51 ± 0.42 N mm,2 at week 20, 1.15 ± 0.26 N mm,2 at week 36 and 0.94 ± 0.31 N mm,2 at week 6 postnatal) but was not significantly correlated with any of the hormones measured. These data suggest that extreme changes in the concentrations of reproductive hormones do not affect the maximum force-generating capacity of young women. [source] Functional anatomy and muscle moment arms of the pelvic limb of an elite sprinting athlete: the racing greyhound (Canis familiaris)JOURNAL OF ANATOMY, Issue 4 2008S. B. Williams Abstract We provide quantitative anatomical data on the muscle,tendon architecture and geometry of the pelvic limb of an elite sprint athlete, the racing greyhound. Specifically, muscle masses, muscle lengths, fascicle lengths, pennation angles and muscle moment arms were measured. Maximum isometric force and power of muscles, the maximum muscle torque at joints and tendon stress and strain were estimated. We compare data with that published for a generalized breed of canid, and other cursorial mammals such as the horse and hare. The pelvic limb of the racing greyhound had a relatively large volume of hip extensor muscle, which is likely to be required for power production. Per unit body mass, some pelvic limb muscles were relatively larger than those in less specialized canines, and many hip extensor muscles had longer fascicle lengths. It was estimated that substantial extensor moments could be created about the tarsus and hip of the greyhound allowing high power output and potential for rapid acceleration. The racing greyhound hence possesses substantial specializations for enhanced sprint performance. [source] Functional anatomy and muscle moment arms of the thoracic limb of an elite sprinting athlete: the racing greyhound (Canis familiaris)JOURNAL OF ANATOMY, Issue 4 2008S. B. Williams Abstract We provide quantitative muscle,tendon architecture and geometry data for the racing greyhound thoracic limb. Muscle mass, belly length, fascicle lengths, pennation angles and moment arms were measured, as were tendon masses and lengths. Maximum isometric force and maximum power were estimated for muscles, and maximum stress and strain were estimated for tendons. Results are compared with other fast quadrupedal runners, and to previously published data in mixed-breed dogs. The implications of the functional adaptations of the greyhound thoracic limb for sprinting performance are discussed. The thoracic limb was found to benefit from a similar proportion of locomotor muscle mass to the pelvic limb, suggesting that it may be used to some extent in propulsion, or alternatively that stabilisation is very important in this animal. Extrinsic muscles, especially latissimus dorsi and pectoralis profundus, were predicted to be powerful and important for generating net positive work during accelerations. Proximal biarticular muscles show specialisation toward preventing collapse of the shoulder and elbow joints to enable strut-like limb function, or some form of dynamic control. Distal muscles did not appear specialised for elastic energy storage, a functional difference to pelvic limb muscles, and the equivalents in horse thoracic limbs. The greyhound thoracic limb appears to possess substantial differences from both that of more ,sub-maximal specialist' quadrupeds, and from the greyhound pelvic limb. [source] Spontaneous Pulmonary Vein Firing in Man: Relationship to Tachycardia-Pause Early Afterdepolarizations and Triggered Arrhythmia in Canine Pulmonary Veins In VitroJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 10 2007EUGENE PATTERSON Ph.D. Introduction: Rapid firing originating within pulmonary veins (PVs) initiates atrial fibrillation (AF). The following studies were performed to evaluate spontaneous PV firing in patients with AF to distinguish focal versus reentrant mechanisms. Methods: Intracardiac recordings were obtained in 18 patients demonstrating paroxysmal AF. Microelectrode (ME) recordings were obtained from superfused canine PV sleeves (N = 48). Results: Spontaneous PV firing (566 ± 16 bpm; 127 ± 6 ms cycle length) giving rise to AF (52 episodes) was observed. Tachycardia-pause initiation was present in 132 of 200 episodes of rapid PV firing and 34 of 52 AF episodes. The pause cycle length preceding PV firing was 1,039 ± 86 ms following tachycardia (420 ± 40 ms cycle length). The remaining episodes were initiated following a 702 ± 32 ms pause during sinus rhythm (588 ± 63 ms). Spontaneous firing recorded with a multipolar mapping catheter did not detect electrical activity bridging the diastolic interval between the initial ectopic and preceding post-pause sinus beat. Tachycardia-pause initiated PV firing (138 ± 7 ms coupling interval) in patients correlated with tachycardia-pause enhanced isometric force, early afterdepolarization (EAD) amplitude, and triggered firing within canine PVs. Rapid firing (1,172 ± 134 bpm; 51 ± 8 ms cycle length) following an abbreviated coupling interval (69 ± 12 ms) was initiated in 13 of 18 canine PVs following tachycardia-pause pacing during norepinephrine + acetylcholine superfusion. Stimulation selectively activating local autonomic nerve terminals facilitated tachycardia-pause triggered firing in canine PVs (5 of 15 vs 0 of 15; P < 0.05). Conclusions: The studies demonstrate (1) tachycardia-pause initiation of rapid, short-coupled PV firing in AF patients and (2) tachycardia-pause facilitation of isometric force, EAD formation, and autonomic-dependent triggered firing within canine PVs, suggestive of a common arrhythmia mechanism. [source] Kinetic strategies of patients with shoulder impingement syndromeJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2010Yan Doiron Abstract Our aim was to determine whether subjects with shoulder impingement syndrome (SIS) have abnormal multijoint torque patterns compared to healthy subjects during normalized isometric force along specific directions. Subjects had to generate an isometric force corresponding to 40% of the maximal pain-free force. Eight targets were displayed on a monitor (0, 45, 90, 135, 180, 225, 270, and 315°). We calculated shoulder and elbow torques (kinetic strategies) using a biomechanical model. Regardless of the target location, the SIS group succeeded in reaching the target; however, when compared to the healthy subjects, they needed more time to do so, suggesting that SIS may slow down the execution of the kinetic strategies. Moreover, the SIS group produced lower shoulder external/internal torque to reach the targets located at 0° and 225°, and they generated greater abduction/adduction torque for targets located at 0, 135, and 180°. In addition, they had lower elbow extension/flexion torque for the target located at 315°. The investigation of atypical kinetic strategies is essential to provide an understanding of the pathomechanics of the SIS and to develop more effective treatment strategies. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:6,11, 2010 [source] Contractile properties of the proximal urethra and bladder in female pig: Morphology and functionNEUROUROLOGY AND URODYNAMICS, Issue 1 2006J.J.M. Pel Abstract Aims To compare the contractile properties of proximal urethral and bladder muscle of the female pig. Materials and Methods In two proximal segments (I and II) of the urethra, small muscle bundles were excised to measure the force-length (maximum force) and the force-velocity (unloaded shortening velocity) relation using the stop-test. The rate of force development was calculated using phase plots. Contractile properties of urethral and bladder segments were statistically compared using the Mann,Whitney U -test. Immunohistochemical staining of whole circumference urethral cross sections was used to identify the location of smooth and striated muscle fibres. Results On isometric force development, the urethral muscle bundles revealed a fast (,0.5 sec) and a slow (,2.1 sec) time constant, whereas in bladder only a slow (,2.3 sec) component was measured. On average, isometric force was highest in bladder. The length range over which force was produced was smallest in urethral segment II, followed by urethral segment I and finally bladder. The unloaded shortening velocity was 0.15, 0.25 and 0.35 1/sec, respectively. Histological preparations showed that smooth as well as striated muscle was present in proximal urethra. In urethral muscle bundles, spontaneous contractions were measured with a frequency of 0.4 Hz. Conclusions Differences in contractility found between urethra and bladder may be ascribed to the presence of striated muscle in the proximal urethra. The regulation of tone and spontaneous contractions may be part of the continence mechanism in the female pig urinary tract. © 2005 Wiley-Liss, Inc. [source] Dihydrotestosterone activates the MAPK pathway and modulates maximum isometric force through the EGF receptor in isolated intact mouse skeletal muscle fibresTHE JOURNAL OF PHYSIOLOGY, Issue 3 2010M. M. Hamdi It is generally believed that steroid hormones have both genomic and non-genomic (rapid) actions. Although the latter form an important component of the physiological response of these hormones, little is known about the cellular signalling pathway(s) mediating these effects and their physiological functions in adult mammalian skeletal muscle fibres. Therefore, the primary aim of this study was to investigate the non-genomic actions of dihydrotestosterone (DHT) and their physiological role in isolated intact mammalian skeletal muscle fibre bundles. Our results show that treating the fibre bundles with physiological concentrations of DHT increases both twitch and tetanic contractions in fast twitch fibres. However, it decreases them in slow twitch fibres. These changes in force are accompanied by an increase in the phosphorylation of MAPK/ERK1/2 in both fibre types and that of regulatory myosin light chains in fast twitch fibres. Both effects were insensitive to inhibitors of Src kinase, androgen receptor, insulin-like growth factor 1 receptor and platelet-derived growth factor receptor. However, they were abolished by the MAPK/ERK1/2 kinase inhibitor PD98059 and the epidermal growth factor (EGF) receptor inhibitor tyrphostin AG 1478. In contrast, testosterone had no effect on force and increased the phosphorylation of ERK1/2 in slow twitch fibres only. From these results we conclude that sex steroids have non-genomic actions in isolated intact mammalian skeletal muscle fibres. These are mediated through the EGF receptor and one of their main physiological functions is the enhancement of force production in fast twitch skeletal muscle fibres. [source] Acute heavy-resistance exercise,induced pain and neuromuscular fatigue in elderly women with fibromyalgia and in healthy controls: Effects of strength trainingARTHRITIS & RHEUMATISM, Issue 4 2006Heli Valkeinen Objective To examine heavy-resistance exercise,induced acute neuromuscular fatigue, blood lactate concentration, and muscle pain in elderly women with fibromyalgia (FM) and in healthy controls before and after a period of strength training. Methods Thirteen elderly women with FM (mean ± SD age 60 ± 2 years) and 10 healthy women (mean ± SD age 64 ± 3 years) performed a heavy-resistance fatiguing protocol (5 sets of leg presses with 10 repetitions maximum) before and after a 21-week strength training period. Maximal isometric force and electromyography (EMG) activity of leg extensors and blood lactate concentration were measured during the loading. Pain was assessed by visual analog scale. Results The strength training led to large increases in maximal force and EMG activity of the muscles and contributed to the improvement in loading performance (average load/set) at week 21. The fatiguing loading sessions typically applied in strength training before and after the experimental period caused remarkable and comparable acute decreases in maximal force and increases in blood lactate concentration in both groups. Acute exercise-induced muscle pain increased similarly in both groups, and the pain level in women with FM was lowered after the 21-week training period. Conclusion The increased strength in women with FM improved high-load performance and also seemed to attenuate perceived pain. Acute exercise-induced neuromuscular changes and the time course of muscle pain in women with FM were comparable with findings in healthy controls, which suggests a typical fatiguing process and a similar trainability of the muscles in elderly women with FM. [source] The Na-K-ATPase is a target for an EDHF displaying characteristics similar to potassium ions in the porcine renal interlobar arteryBRITISH JOURNAL OF PHARMACOLOGY, Issue 5 2002Eckhart Büssemaker The present study was performed to determine the characteristics of the endothelium-derived hyperpolarizing factor (EDHF) that mediates the nitric oxide (NO)- and prostacyclin (PGI2)-independent hyperpolarization and relaxation of porcine renal interlobar arteries. Bradykinin-induced changes in isometric force or smooth muscle membrane potential were assessed in rings of porcine renal interlobar artery preconstricted with the thromboxane analogue U46619 in the continuous presence of N, -nitro- L -arginine and diclofenac to inhibit NO synthases and cyclo-oxygenases. Inhibition of NO- and PGI2 -production induced a rightward shift in the concentration-relaxation curve to bradykinin without affecting maximal relaxation. EDHF-mediated relaxation was abolished by a depolarizing concentration of KCl (40 mM) as well as by a combination of charybdotoxin and apamin (each 100 nM), two inhibitors of calcium-dependent K+ (K+Ca) channels. Charybdotoxin and apamin also reduced the bradykinin-induced, EDHF-mediated hyperpolarization of smooth muscle cells from 13.7±1.3 mV to 5.7±1.2 mV. In addition to the ubiquitous ,1 subunit of the Na-K-ATPase, the interlobar artery expressed the , subunit as well as the ouabain-sensitive ,2, ,3 subunits. A low concentration of ouabain (100 nM) abolished the EDHF-mediated relaxation and reduced the bradykinin-induced hyperpolarization of smooth muscle cells (13.6±2.8 mV versus 5.20±1.39 mV in the absence and presence of ouabain). Chelation of K+, using cryptate 2.2.2., inhibited EDHF-mediated relaxation, without affecting NO-mediated responses. Elevating extracellular KCl (from 4 to 14 mM) elicited a transient, ouabain-sensitive hyperpolarization and relaxation that was endothelium-independent and insensitive to charybdotoxin and apamin. These results indicate that in the renal interlobar artery, EDHF-mediated responses display the pharmacological characteristics of K+ ions released from endothelial K+Ca channels. Smooth muscle cell hyperpolarization and relaxation appear to be dependent on the activation of highly ouabain-sensitive subunits of the Na-K-ATPase. British Journal of Pharmacology (2002) 137, 647,654. doi:10.1038/sj.bjp.0704919 [source] Isometric force development in human horizontal eye muscles and pulleys during saccadic eye movementsACTA OPHTHALMOLOGICA, Issue 8 2009Gunnar Lennerstrand Abstract. Purpose:, The connective tissue elements forming the check ligaments and portals of the human eye muscles have recently been ascribed with a pulley function. Active positioning of the pulleys over orbital layer contraction during eye movements has been suggested. Other studies have instead demonstrated fibrous tissue connections between all parts of the muscle and the pulleys. We aimed to compare the isometric force developed at the muscle tendon and at the pulleys of the horizontal eye muscles, and to investigate which eye muscle structures might exert force on the pulleys. Methods:, Isometric force development was recorded from the lateral and medial rectus muscles in six patients operated for strabismus under topical anaesthesia. Two strain gauge probes were used, each attached with 5,0 silk sutures either to the muscle tendon or to the pulley. The eye muscles were activated by horizontal saccadic eye movements in steps from 30 degrees in the off-direction to 30 degrees in the on-direction of the muscles. Results:, The forces developed at the tendon and pulley were almost identical with respect to amplitude and other parameters. No differences were found in forces developed at the pulleys of the medial and lateral rectus muscles. Conclusions:, The results support the presence of fibrous tissue connections between all eye muscle fibres and pulley structures, rather than orbital fibre control of the pulley. [source] EFFECT OF THE PHOSPHODIESTERASE 5 INHIBITORS SILDENAFIL, TADALAFIL AND VARDENAFIL ON RAT ANOCOCCYGEUS MUSCLE: FUNCTIONAL AND BIOCHEMICAL ASPECTSCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2009Haroldo A Toque SUMMARY 1The anococcygeus muscle is part of the erectile machinery in male rodents. Phosphodiesterase (PDE) 5 inhibitors enhance and prolong the effects of cGMP, which has a key role in penile erection. The aim of the present study was to provide a functional and biochemical comparison of the three PDE5 inhibitors, namely sildenafil, tadalafil and vardenafil, in the rat anococcygeus muscle. 2Muscle strips were mounted in 4 mL organ baths and isometric force recorded. Levels of cGMP were measured using an enzyme immunoassay kit. Western blots were used to determine PDE5 protein expression. 3The PDE5 inhibitors concentration-dependently relaxed carbachol-precontracted anococcygeus muscle; however, vardenafil was more potent (pEC50 = 8.11 ± 0.05) than sildenafil (7.72 ± 0.06) or tadalafil (7.69 ± 0.05). Addition of NG -nitro- l -arginine methyl ester (100 µmol/L) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 µmol/L) to the organ baths caused significant rightward shifts in concentration,response curves for all PDE5 inhibitors. 4Sildenafil, tadalafil and vardenafil (all at 0.1 µmol/L) caused leftward shifts in the glyceryl trinitrate (GTN) concentration-response curves (by 4.0-, 3.7- and 5.5-fold, respectively). In addition, all three PDE5 inhibitors significantly potentiated relaxation responses to both GTN (0.01,10 µmol/L) and electrical field stimulation (EFS; 1,32 Hz), with vardenafil having more pronounced effects. 5All three PDE5 inhibitors reduced EFS-evoked contractions in a concentration-dependent manner over the concentration range 0.001,1 µmol/L. There were no significant differences between the effects of the three PDE5 inhibitors. 6Vardenafil (0.01,0.1 µmol/L) was more potent in preventing cGMP degradation in vitro than sildenafil (0.01,0.1 µmol/L) and tadalafil (0.01,0.1 µmol/L). 7Under control conditions, the expression of PDE5 was higher in the anococcygeus muscle than in the corpus cavernosum. 8In conclusion, PDE5 inhibitors enhance exogenous and endogenous nitric oxide-mediated relaxation in the rat anococcygeus muscle. The potency of vardenafil was greater than that of either sildenafil or tadalafil. [source] Action monitoring in motor control: ERPs following selection and execution errors in a force production taskPSYCHOPHYSIOLOGY, Issue 5 2003Ellen R. A. De Bruijn Abstract Action monitoring has been studied in many tasks by means of measuring the error-related negativity (Ne/ERN), but never in a motor control task requiring precise force production. Errors in discrete choice reaction tasks are the result of incorrect selections, but errors in force production can also arise from incorrect executions. ERPs were obtained while participants produced low or high isometric forces with their left or right hand. As expected, incorrect choices of hand elicited an Ne/ERN. Interestingly, Ne/ERNs were also present in the less discrete selection error of an incorrect choice of force, but only when erroneously a low instead of a high force was chosen. In both force ranges, no Ne/ERNs were found after errors in execution. These errors showed a large positivity in feedback ERPs and, similar to correct responses, a prolonged negativity in response ERPs. We propose that, compared to selection errors, the time uncertainty aspects of execution errors and the resulting changing response representations prohibit error detection by the internal monitoring system responsible for generating the Ne/ERN. [source] | |||||||||||||